Area monitoring devices, such as laser scanners, and other optoelectronic monitoring systems, provide control and safety functions in a wide variety of applications. Laser scanners, for example, are used in fixed installations to safeguard hazardous machine areas, and for collision avoidance in autonomous guided vehicle (AGV) installations.
A typical laser scanner provides control signaling responsive to detecting object intrusions into its monitored “zone.” For example, the laser scanner may include safety-critical output switches that open electrical power to a hazardous machine, responsive to detecting object intrusions. In AGV applications, the laser scanner may activate vehicle braking systems, initiate evasive steering actions, or otherwise inhibit AGV movement, responsive to detecting objects within safety-critical distances of the AGV.
In one aspect of such monitoring, zone monitoring characteristics may need to change dynamically. For example, in a machine guarding application, the laser scanner may be required to monitor a first zone during one phase of machine operation, and monitor a second zone during another phase of machine operation. The physical areas covered by each zone may be the same or at least overlap, but different monitoring parameters may be used, such as different warning and safety-critical distances or different zone boundaries. Similarly, in AGV applications, different zones may be required depending on the AGV's context.
AGV context may be defined, for example, based on one or more detected potential obstacles around the AGV, AGV speed, and AGV location. For example, a large factory environment may include open areas or areas with no human workers, where high AGV speed is permitted, and other areas with potential obstacles or with human workers, where lower AGV speed is mandated. Different monitoring zone configurations are necessary for proper, safe AGV operation in these differing contexts.
Correspondingly, it is known for AGV vehicles to provide dynamically changing zone selection inputs to a laser scanner, to cause the laser scanner to change its monitoring zone during the course of normal operation. Similarly, machine control systems also may provide zone selection inputs to a laser scanner, so that the laser scanner's monitoring zone may be changed over changing phases of machine operation.
As zone selection has critical safety implications, the zone selection inputs of a laser scanner generally include multiple safety-of-design considerations. For example, the use of complementary discrete electrical inputs may be used for zone selection. In this case, the laser scanner may be configured to require inputs—one HIGH and one LOW—before activating a corresponding given monitoring zone. As a result, single fault conditions involving disconnected or shorted inputs may be easily detected and mitigated.
The use of discrete inputs and the requirement for complementary input assertion enhances system safety by eliminating or at least greatly reducing incorrect or inadvertent zone selection. One disadvantage, however, is that there are significant limitations on the number of zones that can be safely selected for a given number of discrete inputs.